Strain and Optoelectronic Tuning in Mixed-Halide Perovskites with Ion Irradiation

Defects usually behave as imperfections in materials that significantly degrade their performance. However, the unusual optoelectronic performance in metal halide perovskites in the presence of defects opens the way for strain and optoelectronic properties tailoring with ion irradiation. Defects and strain engineering is performed in triple-cation mixed halide perovskites using proton irradiation at 1 MeV and different fluences. At intermediate fluence, the initial polycrystalline film compressive strain (-0.15%) can be released, improving exciton lifetimes from about 500 ns to approximate to 1 mu s. In contrast, high irradiation fluence is shown to restore compressive strain leading to sample degradation, with lower lifetime values (approximate to 200 ns). Also, the phase segregation occurring under light illumination between bromine-rich and iodine-rich regions is shown to be defects-mediated as the segregation rate increases by a factor of four for high proton irradiation fluence. The irradiation defects are revealed with low-temperature photoluminescence (PL) through bound exciton radiative recombination mechanisms. The PL temperature dependence gives some insight into electron-phonon coupling mechanism and their modification with ion irradiation.